Restenosis of the peripheral vascular arteries is common, morbid and expensive. Initial therapeutic approaches have focused on pharmaceutical agents, mechanical devices (atherectomy or tissue removing), physical devices (stenting) and gene therapy. None of these have been successful. Nor have the recent success surrounding the use of drug-eluting stents in the coronary vascular system yet been translated to the peripheral vascular system. Restenosis has been the Achilles heel of PTA. The current research has shown that intravascular brachytherapy using afterloaded 192-Iridium sources has a beneficial effect of the treatment of restenosis in femoral and popliteal arteries. The drawback to this technique is that patients who have angioplasty performed in the catheterization laboratory must be transported with catheter in situ to the radiation oncology facility where brachytherapy is performed. The aim of this project is to demonstrate that an intravascular brachytherapy system for treatment of peripheral arteries that uses a low-energy source of 125-Iodine will be as safe and effective as the existing system that uses a high-energy source of l92-lridium, and will be suitable to permit the performance of peripheral intravascular brachytherapy within the catheterization laboratory. The accomplishment of this objective will be demonstrated by a) the design and fabrication of a suitable high activity 125-lodine source in the form suitable for delivery for peripheral intravascular treatment, and b) the completion of studies that evaluate the safety and dosimetric efficacy of the prototype source. The principal benefit of this program will be the development of a source and shielding system that will permit the performance of brachytherapy without movement of the patient and its collateral risk, and keep the patient under the supervision of the cardiologist during the procedure. We anticipate that this development will extend the use of peripheral intravascular brachytherapy to a much larger number of hospital centers.